This invention relates generally to a liquid applicator and more particularly to an apparatus and method for precision application of liquid containing microencapsulated beads of adhesive to a fastener.
In general, it is desirable to apply liquid to a surface. More specifically, it is desirable to affix a patch of adhesive to a fastener, such as a threaded screw. When a screw with a patch containing beads of adhesive engages with matching threads, such as on a nut, the adhesive will be released from the microencapsulated beads or a mixture will occur causing an adhesive to form to secure the screw and nut together forming a fastener arrangement resistent to vibration and other means that may cause disengagement. Various sized patches of adhesive may be used depending on the desired use and applications.
The application of liquid, and especially adhesive, to threads creates a special problem in that precision application of the liquid is required. Too much or too little liquid on the threads will generate a defective patch. Also, precise patch area or coverage is of concern when applying an adhesive patch to a fastener. If a patch strays beyond the desired predetermined area, it will cause problems with the use of that fastener when installed in its intended application. With the use of liquid with microencapsulated beads of adhesive, it is critical not to use excessive pressure in the application of the liquid because of the danger that the microencapsulated beads of adhesive will burst and render the patch unusable. Overall, if the liquid is not gently and precisely applied to the fastener according to the desired specifications to form a patch, the entire fastener will be unusable thereby unnecessarily increasing production and processing costs.
In the past, prior art liquid applicators have been used for the application of various types of liquids to various types of surfaces. The prior art applicators employ various means for controlling and directing the flow of liquid onto the desired surface. To control the flow of liquid, prior art applicators have changed the size of its outlet port to control the flow of the liquid as well as changed the pressure through the applicator to in turn vary the output flow of the liquid from the applicator onto the desired surface. Examples of such prior art liquid applicators are described in detail in U.S. Pat. Nos. 3,972,631, 3,341,354, 3,383,054, and 4,667,879.
The devices for flow control of the prior art applicators are poorly suited for the delicate application of liquid adhesive to a fastener. Most prior art applicators use pressure to force the liquid through the applicator. None of these apparatuses take into account the delicate nature of the liquid. As a result, application under such pressure would burst the microencapsulated beads and prematurely release the adhesive. Prior art applicators that spray the liquid onto the desired surface are similarly ill-suited for fasteners. Undesirable overspray causes the patch to be unusable for its intended purposes. Prior art liquid applicators and methods for applying liquid to fasteners do not serve the specific needs for the precise and controlled application of a liquid having microencapsulated portions to form an acceptable patch on a fastener.